I would leave out the Neon Tetra.
Threadfins and Endler's are compatible if the water is kept close to neutral. Threadfin's prefer slightly acidic, Endler's do best in slightly basic. But I found some authorities who OK their compatibility, so this may not be too critical.
They also both like warmth, high 70's to low 80's F, something the Neons do not, they are cooler water fish, not above 77F.
We have fish profiles, second tab from the left in the blue bar across the top of the page, with many fish species included. The Threadfin Rainbowfish is included, you can click on the shaded name to see its profile. The Neon Tetra is also included.
Here is some info on the Endler, which is not yet in our profiles: Endler's livebearers are nearly all hybrids! | Features | Practical Fishkeeping
The tank setup in our profile for the Threadfin will suit the Endler's too.